M1A1 Stock Common Crack Theory

[frankderrico]

I am fixing the crack in this stock for a member. I was also asked from some members why this is common and is it a fault of the design. I do not believe that it is a fault. I believe that it occurs from the forced removal of the wire portion of the stock. The long bolt with the spring goes through a close fitting collar then into the lower sling swivel that cups on the bottom of the grip. The bolt can seize the collar if it is not lubricated. If someone tries to hit it out, is when I believe the stock cracks. These stocks are very valuable so please keep them lubed and use plenty of caution if you have to take them apart. This particular stock is natural low wood that went through a rebuild at Rock Island sometime between 1947 & 1958. That is when it probably received its MWO ORD B28-W2 modification.

Best Regards.....Frank


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[HDSledge]

Is the washer that sits on top of the hinge screw spacer to compress the spring missing or was it eliminated during the rebuild?



Looking forward to the details and process on the fix. <0

[HDSledge]

While browsing for sale items I noticed this phenom a few times already. If it's not caused from overextending the stock, something else, perhaps the nonlinear arrangement of the grip and forestock is cracking it from the recoil. Deployed the wire stock is not centered at the back but is to the right side. Torque at the opposite corner?

[shadycon]

Could it be caused by a lot of shooting with stock folded?

The hand grip takes all the recoil.

[HDSledge]

Could it be caused by a lot of shooting with stock folded?

The hand grip takes all the recoil.

Makes sense. That is a lot of force transmitted to the grip, resulting in a big jolt of torque to the forestock right at the front edge of the recoil plate. The recoil plate keeps the last inch or so of the forestock contained and stable but when fired the inertia of the action/barrel pits rearward forces against forward forces, trying to jackknife the gun at the recoil plate. The wood on the left side at that area must be thinner or weaker and cracks. Even worse chance if the grip screw is loose, one reason they switched to the longer ones I think.

I'm not sure but I suspect since this mod of the M1 was a rushed item, they may not have anticipated it being fired routinely with stock folded and didn't test the design thoroughly for that case. Wasn't it a space and weight consideration? Almost impossible to aim through a peep sight without a stock to stabilize the gun so surely they didn't expect widespread use without the stock deployed?

Over flexing the stock in the open position could also be a cause but unless someone is willing to destructively test I don't think we will find out. Of course an old solder or ordinance expert might have seen it or heard firsthand how it happened.

I think Shady may have nailed though. Knowing how these go together now I think even a few shots stock folded could crack them at that corner.

[HDSledge]

Noticed something interesting in Frank's pic. I can see how the long hinge screw is on the side that cracks and probably contributes most of the torque. Could be why the left side is cracking and not the right.

Also on the right the recoil plate is firmly held down by a screw. On the left side the recoil plate is not held as firmly to the wood by the hinge screw. It slides through the cap, recoil plate, and grip and screws into the nut on the bottom of the grip.

I imagine if you held the forestock in your hand, took a hammer and hit the hinge screw in the direction of the purple line, the stock would crack right at the corner. The more I look at it the more I think Shady is on target. Mystery solved?

[firstflabn]

Moment, not torque.

[HDSledge]

Moment, not torque.

You got me on that one.: The definition of torque states that one or both of the angular velocity or the moment of inertia of an object are changing. And moment is the general term used for the tendency of one or more applied forces to rotate an object about an axis, but not necessarily to change the angular momentum of the object


But wait: A moment of a force is the same thing as a torque.
I unsurrender.

[browningautorifle]

With a square corner there odds are it will crack, no matter whether it's force or abuse. That's the reason they changed the corner to a circle cut on the M1 rifle op rod. This is the same. A square corner cracks.

[HDSledge]

With a square corner there odds are it will crack, no matter whether it's force or abuse. That's the reason they changed the corner to a circle cut on the M1 rifle op rod. This is the same. A square corner cracks.

I'll bite. If that is the case there should be examples of original M1A1 with cracks on the right side where there is also a corner. All the ones I can find so far have the same crack left side forward of the hinge screw. I am curious if only high wood stocks or ones they milled down during the rebuilds cracked. Did new second production low wood forestocks (that had some changes for stability) also crack there?

The cracked left side ones seem to be very common (can't find any with a cracked right corner) and I haven't seen many without the crack. Here's a low wood for sale at CMP that was milled down from high wood during the rebuild.

And the one that was sold recently on gb as original ($4k) with an obviously repro wire stock. On this one the crack looks repaired, good job, but repaired. Wasn't sure at first but zoomed in no doubt about it.